1. Field of the Invention
The present invention relates to ratchet wrenches and, in particular to reversible ratchet wrenches and the reversing mechanism thereof.
2. Description of the Prior Art
In a reversible ratchet wrench, a reversing pawl mechanism is engageable with a ratchet wheel in either of two conditions, forward or reverse, for respectively accommodating rotation of the ratchet wheel in opposite directions relative to the wrench housing during the back stroke of the wrench. Typically, a reversing member on the housing is coupled to the pawl mechanism for selective shifting thereof between its forward and reverse conditions. As the ratchet wheel rotates during the back stroke, it effects a ratcheting pivoting movement of the pawl mechanism and, since the pawl mechanism is coupled to the reversing member, this typically effects a corresponding oscillating movement or wobbling of the reversing member. This is disadvantageous, in that the operator often applies his palm to the top of the wrench head on which the reversing member is located and, therefore, contacts the reversing lever. When a fastener is being rotated, the user's palm could inadvertently move the reversing lever such that the pawl is moved to a neutral position whereupon the ratchet wheel is no longer restrained, which could result in injury to the user. Further, the reversing lever could be inadvertently retained in a position corresponding to the maximum oscillation during ratcheting resulting in a partial engagement of the pawl mechanism and ratchet wheel. This condition can cause ratchet wheel breakage at lower than expected torque loads upon reapplying load in the forward direction.
Several techniques have been used to prevent movement of the reversing lever during the back stroke of the wrench. One such technique utilizes a pawl mechanism comprising two separate pawls, arranged so that the one which is engaged with the ratchet wheel is decoupled from the reversing lever. An example of this technique is found in U.S. Pat. No. 2,803,980. Another technique utilizes two different bias springs for the reversing mechanism, one to bias the reversing lever to either one of its forward or reverse positions and the other to bias the pawl mechanism into engagement with the ratchet wheel. The spring force of the latter spring is much less than that of the former, so that the ratcheting does not move the reversing member. An example of this technique is found in U.S. Pat. No. 3,265,171. A third technique designs the parts so that the ratcheting movement of the pawl is in a direction relative to the reversing member such that it does not tend to move the latter. An example of this technique is found in U.S. Pat. No. 3,269,496. All of these techniques necessitate the use of relatively complicated mechanisms comprising a relatively large number of parts.